1. Field of the Invention
This invention relates to cleaning and/or drying liquids, and more specifically, to process and apparatus for separating and removing the aqueous phase from the oil phase of spent cleaning and/or drying liquids.
2. Description of the Prior Art
Solutions of surfactants in liquid chlorocarbons and chlorofluorocarbons capable of solubilizing water have found important industrial uses. Employed as cleaning liquids, such solutions containing solubilized water are frequently capable of dissolving not only those soils which are soluble in the chlorocarbon or chlorofluorocarbon but also those which are usually soluble only in water. Frequently, such solutions are also capable of emulsifying insoluble soils. The unusual properties of these liquids have led to their extensive use in cleaning, such as in the cleaning of industrial articles, and in the drycleaning of textile materials. Liquids of this kind and which are not saturated with respect to solubilized water have also been employed for the drying of water-wet articles in processes wherein the water adhering to the articles is solubilized by the liquid mixture.
Solutions comprising a chlorofluorocarbon, particularly 1,1,2-trichloro-1,2,2-trifluoroethane, are known in the art for the cleaning and/or drying of sensitive materials, such as plastic electronic assemblies. Swiss Patent 445,001 includes a disclosure of such a solution. Chlorocarbons, because of their greater aggressiveness, are often not suitable for such a use. Of the liquids described in the Swiss patent, the combination of 1,1,2-trichloro-1,2,2-trifluoroethane, about 2 weight % of isopropylammonium dodecylbenzenesulfonate as surfactant and about 6 weight % of solubilized water has been employed in the trade, particularly for the cleaning of, and sometimes for the drying of, precision metal parts and plastic articles. The patent further discloses that small amounts of aqueous ammonia can be added for special cleaning purposes and that specified inhibitors can be added to prevent reaction of the composition with reactive metals. Such liquids comprising a chlorocarbon or chlorofluorocarbon, a surfactant and solubilized water may be unstable toward electrolytes. Hence, in uses wherein such a liquid imbibes electrolytes from the articles being cleaned or dried, the liquid becomes spent. As the term is used herein, a spent liquid or solution is one wherein some of the solubilized water has separated from the oil phase to form an aqueous phase. The Swiss patent discloses that, to restore the spent cleaning and/or drying liquid to usefulness, the aqueous phase, which contains most of the electrolytes, should be separated (from the oil phase) and discarded and, optionally, fresh water should thereafter be added to the oil phase and, optionally, to overcome operational losses, an appropriate amount of 1,1,2-trichloro-1,2,2-trifluoroethane should be added. In overcoming operational losses, the make-up liquid usually employed consists of 1,1,2-trichloro-1,2,2-trifluoroethane and a surfactant which is dissolved therein at a concentration equal to about one-third to one-half of the surfactant concentration in the original drying and/or cleaning liquid. In connection with the optional addition of fresh water, publicly available water supplies are generally of sufficient purity for the regeneration of spent liquids. For drying liquids, it is to be understood that water should not be added to the oil phase.
The above-described restoration process for spent liquids does not remove soils dissolved in the oil phase. However, since the appearance of an aqueous phase generally occurs much before the liquid is overloaded with chlorofluorocarbon soluble soils, regeneration of the oil phase, as described above, substantially extends the useful life of the liquid. In other words, the liquid can be regenerated one or more times before there is objectionable buildup of soil.
Cleaning and/or drying liquids other than those described above but comprising a chlorofluorocarbon and an alkylbenzenesulfonate surfactant also are known in the art. For example, amine-neutralized undecyl- and tridecyl-benzene-sulfonic acids are surfactants for the solubilization of water in trichlorofluoromethane, 1,1,2,2-tetrachloro-1,2-difluoroethane or 1,1,2-trichloro-1,2,2-trifluoroethane. Such compositions are useful as cleaning and/or drying liquids. It is also known that non-ionic surfactants can be advantageously added to the aforesaid undecyl- and tridecyl-benzene-sulfonate chlorofluorocarbon compositions and mixed amine salts of dodecylbenzenesulfonic acid are known to be suitable as surfactants in trichlorotrifluoroethane. Such compositions also are useful as cleaning and/or drying liquids.
Surfactants other than alkylbenzenesulfonates are also known to be useful for the solubilization of water in chlorofluorocarbons and, thus, for the formulation of cleaning and/or drying liquids. For example, solutions of alkali metal salts of dioctyl sulfosuccinate in 1,1,2-trichloro-1,2,2-trifluoroethane and the corresponding amine salts in chloro- and bromo-hydrocarbon solvents exhibit such utility.
Of the above-described liquids or solutions, those which are most useful as cleaning and/or drying liquids are those wherein the surfactant tends to remain in the oil phase, thus minimizing loss of surfactant in the aqueous phase which is discarded. The alkylbenzenesulfonates exhibit this property and, for this reason, generally are preferred. Trade use of the above-described liquids has been hindered by difficulties which are inherent in known methods for regenerating spent liquids.